Various circuits are known which convert a temperature into a corresponding frequency value so that a temperature change can be detected by sensing the frequency. Such circuits typically have a nonlinear temperature or output response. This makes it impossible to provide a satisfactory temperature compensation in a watch, for example, if the detected output is directly utilized. Therefore, it is necessary that the output response be linearized.
Conventional linearizing means may be categorized into two types, the first in which the response of an element itself is made linear, and the in which the response of the element is digitalized through A/D conversion, which is then subjected to a linearization process. The former type may be exemplified by a combination of a temperature element, for example, a thermistor and a fixed resistor, which is connected in a bridge so that a linear output may be obtained in response to a temperature change. While a linear output response may be obtained with this arrangement, an increased number of additional components such as resistors is required, and also the circuit module increases its size, which is inconvenient for incorporation into an electronic watch, in particular. Additionally, variations in the operational response of the temperature detector circuit as well as of the additional components prevent an output response having a high stability and high linearity from being obtained.
In the latter type, an output from the A/D conversion is utilized to address a read only memory (ROM) to retrieve a corresponding linearized value. Those skilled in the art will appreciate that this results in an extensive system arrangement, lacking in flexibility due to the provision of the ROM.
The accuracy of the electronic watch has been markedly improved since the advent of the quartz oscillator which is used as a oscillator source. However, the quartz oscillator exhibits a temperature-frequency response which is parabolic. This means that while the accuracy of the quartz watch remains stable in a temperature range which corresponds to the apex of the response, the accuracy is less than satisfactory in other temperature ranges. Accordingly, a number of compensation techniques have been proposed to compensate for the temperature response of a quartz watch or a quartz oscillator.
One of proposed temperature compensation techniques employs a capacitor which exhibits a complementary response to the parabolic temperature response of the quartz oscillator and which is connected in an oscillation loop to provide a compensation for the temperature response of the quartz oscillator. However, the degree of accuracy which can be achieved with this technique is limited because a capacitor having a temperature response which is perfectly complementary to that of the quartz oscillator is not available. In addition, the use of a capacitor suffers from disadvantages associated with aging effects and an increased temperature hysteresis.
To overcome such difficulties, there has been proposed the use of a temperature sensor, the output of which is utilized to improve the temperature response of the quartz oscillator in a digital manner. A temperature sensor which has been used in the prior art at this end comprises a quartz oscillator exhibiting a different temperature response from that of a basic oscillator source. The principle of operation is based on deriving a beat signal between outputs from a reference or source oscillator and an oscillator circuit of a temperature sensor. However, quartz oscillators used to form the respective oscillators must have temperature responses which are in a given relationship. As a result, the choice and adjustment of these quartz oscillators and associated components such as capacitors represent a troublesome procedure, resulting in increased cost and increased power dissipation. In addition, when a pair of quartz oscillators exhibiting parabolic temperature responses which have their individual peaks at different temperatures are used, there is a difficulty, in addition to the choice of these quartz oscillators, in that the oscillators must be trimmed to provide an equal oscillation frequency at the apex temperatures. This requires time and labor, but the trimming accuracy is still poor enough to prevent a temperature compensation of a high level from being achieved.
It is a principal object of the invention to overcome above disadvantages by providing a novel and improved linearizer circuit and an electronic watch utilizes such circuit as a temperature detector.
It is another object of the invention to provide a linearizer circuit which facilitates it implementation into a watch by dispensing with external components and facilitating the integration, thereby providing a simple arrangement, a stable characteristic and a high level of flexibility.
It is a further object of the invention to provide an electronic watch in which a reference clock pulse is utilized to produce temperature information in a digital form, thereby enabling a temperature compensation of a high accuracy for the stepping rate while reducing external components required to such compensation to facilitate the integration and minimizing the power dissipation.